Did you place any roling stock on your route?  Unless you do, Trainz won't save a 'Session', and routes without sessions don't appear on the list in Driver.  Can you see your route on the list in Surveyor OK?
Also 'British Midlands' is the name of one of the built-in routes.  It's probably going to cause problems if you use the same name for your on creation.
Paul
p.s. Unless you mean you created your own session for the built in route, in which case I don't know what happened...